The present invention relates to onboard apparatus for weighing the load on a truck or the like and, more particularly, to an onboard scale for use on trucks and the like to measure movement between a frame supported above an axle by a compressible suspension system to calculate the load weight being carried by the frame, wherein the scale comprises a sensing member adapted for mounting to the frame and including a load cell for producing at an output thereof an electrical signal proportional to a force applied to an input surface thereof; a contacting member adapted for mounting to the axle and including a movable member adapted to contact the input surface of the sensing member as the frame moves towards the axle under a load compressing the suspension system; and, proportional bias means for biasing the movable member and the input surface towards one another and for applying a proportional force against the input surface as the frame moves towards the axle so that the electrical signal is directly proportional to the weight on the frame and can be used to drive a display indicating the weight.
Onboard weighing apparatus is old and well known in the art. It was recognized at an early time that where a wagon or truck bed was suspended above an axle by a compressible suspension system employing springs, or the like, as load was added, the springs compressed and the bed moved towards the axle. In the extreme, the bed would finally come to rest on the axle. It was also recognized that a rudimentary linkage arrangement could be used to provide an indication of the amount of relative movement and, thereby the amount of weight on the wagon or truck.
With the advent of modern large truck trailers and super highways with load limitations and police enforcement thereof, the ability to provide quick and easy determination of present loading became more important and the attempts to provide a workable onboard weighing system continued. Representative examples of prior art systems for the same or similar purposes can be seen with reference to the following U.S. Pat. Nos. 14,475; 1,432,631; 2,129,343; 2,769,967; 2,779,013; 3,409,097; 3,531,766; 3,603,418; 3,646,512; 3,858,173; 3,867,990; 3,960,228; 4,106,579; 4,219,088; 4,287,958; and 4,375,839.
The prior art systems for onboard weighing have been subject to numerous problems that did not make them practical. Some were designed to be virtually built into the suspension system itself. Others incorporated numerous moving parts and linkages such that they might work well for a limited time under static conditions, but soon bound up or wore out when subjected to the dirt and frictional conditions of constant over-the-road driving. Others were of marginal accuracy due to drift in response to variations in temperature conditions that can find trucks going from subzero conditions in the north to road temperatures well over one hundred degrees in the southwest in a matter of days. The problems could be summed up as one or more of the following: not accurate; not reliable; vehicle installation not practical; breakage problems due to continuous operation, and especially due to vibration and shock, in some cases, installation requiring welding and cutting of the vehicle parts such as the axle and chasis, thus causing fatigue and possible rapid failure of the truck parts themselves.
Wherefore, it is the object of the present invention to provide an onboard scale for weighing the load on a truck or the like which is simple, reliable, easily added or removed, and resistant to dirt and temperature conditions of constant over-the-road driving.